1. Field of the Invention
The present invention relates generally to fire protection and suppression systems and, in particular, to a fire protection and suppression system for protecting a structure from interior or exterior fire threats using passive microwave radiation reception, for example, a structure including a glass curtain wall.
2. Description of the Related Art
Aircraft terminal structures, such as passenger corridors leading to parked airplanes, are sometimes faced with the threat of fire. These threats include natural, accidental, or intentional events, such as in the refueling operations of aircraft, the operation of emergency power generators using nearby, stored liquid or gaseous fuels or intentional criminal assaults on the structure. Other structures faced with similar fire threats include airport hangars, other maintenance buildings, rental car facilities, parking lots and hotels that may be typically present at airports. Outside an airport setting, state, local and federal government agency buildings including embassies in foreign countries may be the target of an intentional fire threat.
It has been estimated that since 1961 there have only been a total of eight aircraft damaged during refueling while there have been thousands of fuel spillage events worldwide. Injuries related to refueling of aircraft are rare. It is also rare but known that aircraft landing at an airport may collide with aircraft preparing to take off or may collide with objects, inadvertently drive off a runway and in at least one instance, overrun a length of runway and land in a body of water. The limited history of airport fires and accidents is testimony to the safety procedures in place at airports worldwide. Nevertheless, there have been embassy and hotel bombings and other criminal assaults and the like on structures involving fire events that have in fact proved damaging to the structures involved and resulted in the loss of human lives.
Many structures are protected from internal fires through an interior fire suppression system, such as interior automatic sprinkler systems. Exterior protection systems are more rare. Valuable structures are often left unprotected from exterior fire threats such as radiant heat generated from a fuel fire during aircraft refueling operations, exposure from fires in neighboring structures, or burning embers that are blown onto the structure from a nearby fire, for example, a brush or forest fire. Intentional fire threats may include but not be limited to the intentional use of a so-called Molotov cocktail as an example. Unprotected structures frequently may include window structures that may comprise glass curtain structures having a height in excess of one story and a width in excess of tens of feet or meters. Indeed, some airport terminals are designed to provide a continuous glass curtain structure in both a main terminal area and along concourses to aircraft gates where aircraft load and unload passengers. Especially hotel lobby areas are often similarly provided with large window curtain structures at their entrances facing a street. Such glass structures may be the weakest structures in the face of fire and break inwardly in the event of a fire threat such as a fuel explosion or exposure to elevated levels of radiant heat from fuel fires or other exterior fire or severe heat exposures, especially single pane glass windows. Window breakage permits unabated direct exposure of a building's interior and its occupants to potential flames and superheated products of combustion, thereby jeopardizing the life safety of the occupants and the building itself.
When an aircraft passenger terminal is faced with an impending fire, particularly those in which large panes of glass are the only barrier between the passengers traversing interior corridors and awaiting a parked aircraft, the resources available to local firefighters are limited. The interior sprinkling system may not activate in a timely manner due to an exterior fire and lives and property inside the terminal may be lost. Moreover, manual actuation of a sprinkling system intended to protect interior (or exterior) glass panes may be required and may be forgotten by untrained airport personnel. Airport fire personnel may arrive too late to save lives and property. Known exterior fire sprinkler systems include so-called water curtain systems which utilize solenoid valves to control a plurality of spaced water spray nozzles to establish a protective curtain of water. Such water curtain systems are utilized, for example, on board off-shore oil rigs to separate, for example, an intentional gas burn-off from personnel and property on the rig. Such water curtain systems require a considerable water flow, not typically available to other facilities. An oil rig has an unlimited supply of water from, for example, an ocean or gulf while an airport may rely on decorative ponds or water supply tanks to supplement a city water main. A hotel building may have to rely only on a city water main for a sprinkler system water supply. On the other hand, a water curtain may be established on a window by a directed spray of water permitting the water to equally flow by gravity down a glass surface.
For example, extinguishment of an impending fire during a refueling operation of a parked aircraft may be limited to the availability of responding firefighters from a nearby station. During the time to detect, notify, and initiate firefighting operations, an incipient fire may grow in size as to severely impact exposed passenger corridors, causing breakage of unprotected large glass windows as well as damaging other exterior structural elements, aircraft, vehicles and airport personnel. Once the fire enters the terminal corridors, conditions become untenable for passengers and other occupants. On the other hand, internal fire sprinkler systems may finally actuate automatically due to internal fire and smoke sensors or manually by airport personnel noticing the external fire.
Fire protection engineering concentrates on the detection of both flaming and smoldering fire signatures, typically through the design of heat, smoke, and optical detectors and combinations of such detectors and arrays. Flame and radiation detectors can be used to monitor for the presence of sparks, burning embers and flames. Ultraviolet and infrared detectors can also be used to detect fire by sensing electromagnetic radiation at ultraviolet and infrared frequencies. An example of a flame detection apparatus is represented by WO 2005/052524 and products available from Micropack (Engineering) Limited of Scotland. The fire detection apparatus includes a closed circuit television system for protecting an area in the field of view of a camera. The lens to the camera is intentionally filtered to receive at, for example, 761 nm in order to be able to distinguish sunlight from a hydrocarbon fire. Moreover, control electronics may provide image analysis known in the art to recognize a real fire while ignoring unwanted alarms. Flame detection generally in the ultraviolet or infrared or combination light range of frequencies is susceptible to false alarms such as intentional setting off of flares, lightning and the like.
Thermal sensing differentiates a temperature of an object from that of a predetermined steady state. For example, U.S. Pat. No. 6,724,467 to Billmers et al., describes a system and method for viewing objects at a fire scene by discriminating reflections from an object from smoke and fire. Some limited tests also have utilized acoustic sensors for fire detection.
Consequently, thermal and flame sensors are often used in combination with smoke detectors. Smoke detectors operate upon the detection of particulate matter from smoke in the air. Particle and smoke detectors use photoelectric, ionization, carbon monoxide, gas-sensing, and photo beam technologies to sense byproducts of combustion. However, these devices also are not infallible, and may falsely trigger from, for example, cigarette or cigar smoke. Moreover, one or both of the thermal and smoke detectors may be slow to react to a growing fire, thus leading to greater risk to property or life. In addition, the presence of smoke can complicate the detection of fires. Studies show that 90% of wood smoke particles are smaller than 1 micron in size. Particles from oil smoke are in the 0.03 to 1 micron range, while particles from cooking smoke from grease are in the 0.01 to 1 micron size, as is tobacco smoke. Consequently, discrimination among types of smoke is difficult. Discrimination may require sophisticated pattern recognition algorithms and detector sensors to reduce the nuisance sensitivity (see L. A. Cestari, et al., “Advanced Fire Detection Algorithms using Data from the Home Smoke Detector Project,” Fire Safety Journal, 40 (2005), 1-28). In an airport or hotel exterior environment, smoke from an external fire may be subjected to wind flow and so smoke detectors, even those located proximate to a refueling fire or intentional fire, may not detect the fire.
Electromagnetic waves are created when charged particles such as electrons change their speed or direction. These electromagnetic waves consist of an electric field and a magnetic field perpendicular to the electric field. The oscillations of these fields are reflected in the frequency and wavelength of the electromagnetic wave. The frequency is the number of waves (or cycles) per second. The energy of these waves may also be characterized in terms of the energy of photons, mass-less particles of energy traveling at the speed of light that may be emitted at certain discrete energy levels. The following mathematical relationship demonstrates a relationship among the wavelength of an electromagnetic wave, its frequency, and its energy:
  λ  =            c      f        =          hc      E      where
λ=wavelength (meters)
c=speed of light (3×108 meters per second)
f=frequency (Hertz)
h=Planck's constant (6.63×10−27 erg-seconds)
E=energy of the electromagnetic wave (ergs)
Wavelength and frequency are the inverse of one another as related by the speed of light, and may be used interchangeably herein in the description of embodiments and the claims as equivalents of one another. Note that the energy of an electromagnetic wave is proportional to the frequency and is inversely proportional to the wavelength. Therefore, the higher the energy of the electromagnetic wave, the higher the frequency, and the shorter the wavelength.
The spectrum of electromagnetic waves is generally divided into regions or spectra, classified as to their wavelength or, inversely, as to their frequency. These bands of wavelengths (frequencies) range from short to long wavelengths (high to low frequency) and generally consist of gamma rays, x-rays, ultraviolet, visible light, infrared, microwave, and radio waves. The term “microwave” generally is used to refer to waves having frequencies between 300 Megahertz (MHz) (wavelength=1 m) and 300 Gigahertz GHz (wavelength=1 mm). Microwave radiation is highly directional, and the higher the frequency, the more directional the emitted radiation.
The radiation from electromagnetic waves can be emitted by thermal and non-thermal means, depending upon the effect of the temperature of the object emitting the energy. Non-thermal emission of radiation in general does not depend on the emitting object's temperature. The majority of the research into non-thermal emission concerns the acceleration of charged particles, most commonly electrons, within magnetic fields, a process referred to in the astrophysics field as synchrotron emission. For example, astrophysicists and radio astronomers look for synchrotron emissions from distant stars, supernovas, and molecular clouds.
On the other hand, thermal emission of radiation from electromagnetic waves depends only upon the temperature of the object emitting the radiation. Raising the temperature of an object causes atoms and molecules to move and collide at increasing speeds, thus increasing their accelerations. The acceleration of charged particles emits electromagnetic radiation which forms peaks within the wavelength spectrum. There may be a direct correlation in changes in temperature impacting the accelerations of the composite particles of an object with the frequency of the radiation and peaks within the spectrum. Once an object reaches its equilibrium temperature, it re-radiates energy at characteristic spectrum peaks. Such microwave radiation will be referred to herein as spectral microwave radiation to distinguish from black body radiation which is an inherent property of different objects, plant and animal life.
Prior attempts to create an exterior fire suppression system have proven to be impractical. For example, U.S. Pat. No. 3,576,212, entitled “FIRE-SHIELDING DEVICE,” which issued on Apr. 27, 1971, describes a system in which four structures are installed adjacent to each of four exterior walls of a building. Each structure extends from the ground to a height above the roof of the building and includes a pipe that is connected to a water source at the bottom of the structure. At the top of each structure is a pair of sprinkler heads, one designed to spray water in a horizontal direction and another designed to spray water in a high arc to be spread over the roof, for example, by the wind. Such a structure may be useful to protect an aircraft terminal building or hotel roof.
Another approach is described in U.S. Pat. No. 5,263,543, entitled “EXTERNAL FIRE PREVENTION SYSTEM,” which issued on Nov. 23, 1993. In this patent, a water pipe is run up the side of a building and connected to another pipe that lies across the top of the roof. The second pipe includes a plurality of sprinklers that are spaced apart. A smoke detector is placed on the side of the building to detect an approaching fire and automatically activates and deactivates the external fire prevention system in the event of detection of smoke. Such a system may protect the roof of an airport terminal or other structure in the event of a significant fire event detected by a smoke detector.
Known airport safety procedures include bonding and grounding an aircraft to be refueled to a refueling tanker truck or a pump vehicle for an underground fuel storage tank. Moreover, the electrical systems of an aircraft to be refueled may be shut down during refueling. Use of radio frequency devices and other electrical devices such as any electrical switch may be restricted during fueling operations. Sprinkler systems are known that are buried underground and pop up to douse fires with an arc of water emitted from pop-up nozzles. These can be used to protect aircraft and vehicles from fire spread but can consume much water and may require underground water tank storage. Such safety measures have decreased the number of fires during refueling and such sprinkler systems decreased the severity of fire damage. On the other hand, owners of hotels and other structures that may have large glass exterior surfaces and hotel managers are generally not capable of controlling the events that occur outside the hotel premises. Moreover, the possibility still exists that an unforeseen event will occur at an airport notwithstanding the safety measures in place to prevent it.
Dr. Vytenis Babrauskas has yearly, since 1996, published his article: “Glass Breakage in Fires,” available from Fire Science and Technology Inc. In it, Babrauskas describes that ordinary flat glass tends to crack when the glass reaches a temperature of about 150-200° C. A window subject to an outside fire is primarily impacted by radiation. While local gas temperatures may be near-ambient, vapor laden air from a fuel spill may result in an explosion or significant overpressure leading to a rupture and unintended ignition, not discussed by Babrauskas, such that there may be no convective cooling flow along a glass surface as the radiant heat is transported by a velocity toward the glass.
Andrew Kim in his paper, “Protection of Glazing in Fire Separations by Sprinklers,” Interflam '93, pp. 83-93 provides results of testing protecting of tempered and heat-strengthened glass by providing a water film on the assembly. Kim describes two primary factors for successful protection: early activation and sufficient water spray. Activation in less than one minute provided for no failure in over one hundred twenty minutes when a sprinkler is mounted at top center of the tempered glass. Internally fed misting nozzles are available for mounting at top center of exterior windows with, for example, a 160° spray pattern that may conserve water but still provide a sufficient water film.
Custer et al., Miami Airport QTA: risk-informed performance-based fire protection,” The Arup journal, 2/2005, pp. 44-47, provides the results of a computer simulation of the explosive range of a gasoline leak from a fueling station after 120 seconds. FIG. 2, at page 46, tends to show a washing effect on a face of a gate structure of a Miami airport concourse model with a pass-through to the other side of the passenger concourse model portion. The model shows that the concourse may receive fire and explosive impact temperatures along an approximately 50 meter distance on either side of a fuel explosion measured perpendicularly to the concourse (typically an elongated, narrow structure of hundreds of meters in length). As a consequence, Custer et al. recommend ultraviolet and infrared sensors to detect flame in fuel dispensing areas.
Referring to FIGS. 2A and 2B, the results of a fire dynamics simulator model utilized by Ryder et al. will be discussed as described in Consequence Modeling Using the Fire Dynamics Simulator, NIST, 2003, 9 pages. FIGS. 2A and 2B represent the results of a simulation of a large (15 m diameter) pool fire of jet fuel. Radiant flux was measured at approximately 17 and 25 meters from the pool. As can be seen from a comparison of FIGS. 2A and 2B, the impact of wind on the results dramatically increased the amount of radiation seen by the target and where the target was 8 meters away, it was engulfed by fire. Unburned vapors extended beyond the diameter of the pool and effectively increased the size of the fire. As can be seen from FIG. 2A, after approximately 100 seconds, a radiant temperature in no wind exceeded 200° C. In the presence of wind per FIG. 2B, the results were less predictable and scattered and the temperature increased from 20° C. at about 20 seconds to 140° C. at 120 seconds and then dissipated. These results are consistent with the Custer et al. model results. Convective heat transfer via wind in both models would appear to impact flux flow and radiative transport may be considered more significant in a no wind environment.
Typical fueling regulations in place at airports such as the Denver Municipal Airport impose additional restrictions to bonding/grounding and the like described above including distance restrictions on airport personnel from smoking and distance restrictions, on the order of 50 feet, from fueling operations from the airport terminal, automatic shut-off valves, shutting down of aircraft engines and equipping tanker trucks and the like with anti-spark exhaust systems. Hotels and other structures with large glass structures may not so impose restrictions on the public passing on public streets. Both Denver and Baltimore Washington International airports utilize fuel containment systems. By sloping the tarmac proximate a refueling location away from the refueling activity and terminal building, fuel may be caused to drain to fuel containment tanks buried in the tarmac and located outwardly from the terminal building.
Referring now to prior art FIG. 1, wherein similar reference numbers are used to represent similar elements of FIG. 3 and other figures relating to embodiments and various aspects, the first number of a reference number represents the figure number wherein the element first appears. In FIG. 1, a refueling operation at Baltimore Washington International (BWI) airport is shown. The depicted refueling operation utilizes a fuel pumping cart 105 for pumping fuel under control of controller 130 located where the fuel enters the plane wing at fuel entry point 115. Cart 105 is moved to a refueling underground fuel hydrant location and is placed there by a vehicle which has been removed from the scene. A controller 130 is operated by an airport employee for operating the pumping cart 105 once the fuel lines are connected to the plane wing fuel entry point 115 from the cart 105 and from the cart 105 to the underground tank in the proximity of the cart 105. The controller 130 provides an indication of electrical bonding of wing to cart and grounding of both and an emergency cut-off, for example, for use if the airport employee notes a fuel spill.
With continued reference to FIG. 1, BWI airport has a deluge sprinkler system for its exterior windows 110. Combination rate-of-rise, fixed temperature thermal detectors 140 are located approximately every other window pane which operate, for example, at a rate-of-rise of 15° F. per minute or a fixed temperature of one of 135° and 194° F. These are shaped as half-moons, flat side down, such that heat thermally conducted up a pane is captured and its temperature sensed. When the temperature rate of increase exceeds a predetermined level or the maximum predetermined fixed temperature limit is exceeded, a signal is transmitted to a fire control panel, which automatically releases a fire sprinkler deluge valve is actuated which delivers water to adjacent sprinkler heads 135. A disadvantage of the BWI system is the requirement for a large number of combination rate-of-rise, fixed temperature detectors and the limitations of mere thermal sensing without utilizing other thermal event detection alternatives including flame and smoke detection.
Airport hangars such as those at Dubai International Airport and Singapore Airport are protected for under-wing fires by mounting fire detectors at below wing height, for example, at 3 meters. For example, three band infrared camera detection of fires under an airplane wing may be used at this height. Hangars typically have very high ceilings and a smoke detector and associated sprinkler system deployed at ceiling height is less effective than one at lower height. A smoke detector, for example, mounted on a ceiling may take valuable minutes to detect a fire while using UV/IR flame detection can cut the detection time to ninety seconds. A hotel lobby may be analogous and have high ceilings. Consequently, it may be appropriate to provide UV/IR flame detection and heat detection as preferred detection means for high ceiling structures. Sprinkler systems may cause considerable damage and require gravity flow to reach a fire. Water may be delayed in falling due to evaporation and air resistance. Consequently, more time may be needed for water or foam/water to reach a fire from a high ceiling than from a sprinkler system at a lower height. Typical water pressures may be set above 250 kPa to provide an initial downward velocity to fire retardant for sprinkler system operation to speed the retardant's reaching a fire below.
These and other prior art approaches suffer from many drawbacks including false alarms that have prevented the widespread implementation of exterior and interior fire suppression systems, particularly to protect aircraft terminals, hotels, hangars with valuable contents, airplanes and other structures, for example, that may be equipped with large glass curtain structures. For example, no such systems exist that allow for the detection of incipient fires using passive microwave detector arrays that may operate to detect fires in all ranges of weather and climatic conditions and through typical walls and obstacles.
A German 2001 NIST paper suggests that Daimler Chrysler Aerospace AG conducted earlier experiments in fire detection using microwave energy (T. Kaiser et al., “Is Microwave Radiation Useful for Fire Detection?” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE '01, Volume 965, Mar. 26-28, 2001, Gaithersburg, Md., NIST Special Publication). The purpose of these experiments, which is not further explained, was to detect fires in garbage bunkers. The possibility of using microwave engineering technologies in passive fire detection is also described in the NIST Conference paper in 2001 by Kaiser et al. which further describes the use of microwaves to passively detect a fire using a conventional Dicke switch operated at 1 KHz to compare a reference temperature of a room wall with measurements at 11 GHz in the microwave region and a bandwidth of 1 GHz. (See R. H. Dicke, “The measurement of thermal radiation at microwave frequencies,” Rev. Scl. Instr. Vol. 17, pp. 268-275, 1946). The discussed technique relies upon thermal radiation from fires generating a detectable signal in the microwave portion of the electromagnetic spectrum. To do so, Kaiser et al. further suggest use of a commercial satellite dish and a superheterodyne low noise converter to measure the microwave radiation of a target test fire.
Kempka et al. in 2006 expand the work of Kaiser et al. to detection and sensing from the use of infrared and microwave at 11 GHz to frequencies from 2 to 40 GHz (T. Kempka et al., “Microwaves in Fire Detection,” Fire Safety Journal, Volume 41, 2006, pp. 327-333) in the microwave spectrum. According to this 2006 publication, thermal radiation may be measurable utilizing four broadband antennas to cover four separate frequency bands of operation, i.e., 2-12, 12-18, 18-26, and 26-40 GHz bands of operation and respective bandwidths at 100 MHz each, “For each configuration one sample will be measured in the first frequency band. Then the receiver changes to the next frequency band and takes another sample. After all the selected frequency bands are measured, the receiver will measure the first band again.”
In view of the drawbacks in the prior art, there is a need for an improved exterior fire suppression system, particularly in aircraft passenger terminals and such structures as hotels with large glass curtain structures to protect personnel and property as well as the structure itself during a fire event.